1. Technical Field
The present invention relates to a rotation angle detection device mainly used for rotation angle detection of a steering wheel of an automobile and the like.
2. Description of the Related Art
In recent years, while functions of an automobile is advanced, automobiles in which a rotation angle of a steering wheel is detected by a rotation angle detection device and various controls of a vehicle are performed with the rotation angle are increasing.
Such a conventional rotation angle detection device will be described with reference to FIG. 5.
FIG. 5 is an exploded perspective view of the conventional rotation angle detection device. In FIG. 5, a reference sign 1 denotes a synthetic resin rotation body in which spur gear portion 1A is formed on an outer periphery of a side surface. A pair of engagement portions 1B to be engaged with a shaft of a steering (not shown) to be inserted is formed on an inner periphery of a center cylinder part of rotation body 1.
A reference sign 2 denotes a synthetic resin first detection body in which spur gear portion 2A is formed on an outer periphery of a side surface. A reference sign 3 denotes a synthetic resin second detection body in which spur gear portion 3A having the different number of gear teeth from spur gear portion 2A is formed on an outer periphery of a side surface. Spur gear portion 2A of first detection body 2 is meshed with spur gear portion 1A of rotation body 1, and spur gear portion 3A of second detection body 3 is meshed with spur gear portion 2A of first detection body 2.
Concave and substantially-rectangular accommodation portion 2B is formed in a center of first detection body 2, and concave and substantially-rectangular accommodation portion 3B is similarly formed in a center of second detection body 3. Cuboid magnets 4A, 5A are respectively accommodated in accommodation portions 2B, 3B.
Further, a reference sign 6 denotes a synthetic resin holder. Biasing portion 6A extends downward from a one side end of a top surface of holder 6. Grip portions 6B are formed so as to extend downward from both sides of holder 6. Magnets 4A, 5A are respectively installed so as to be retained and fixed in accommodation portions 2B, 3B by holders 6.
A reference sign 7 denotes a wiring substrate arranged on the upper side of first and second detection bodies 2, 3 substantially in parallel. A plurality of wiring patterns (not shown) is formed on upper and lower surfaces of wiring substrate 7. Magnetism detection elements 4B and 5B are respectively installed on a surface of wiring substrate 7 facing magnet 4A installed in the center of first detection body 2 and magnet 5A installed in the center of second detection body 3.
First detection means is formed by magnet 4A and magnetism detection element 4B facing each other in such a way, and second detection means is similarly formed by magnet 5A and magnetism detection element 5B. Further, control means 8 connected to magnetism detection elements 4B and 5B is formed by an electronic part such as a microcomputer in wiring substrate 7, so that the rotation angle detection device is formed.
The rotation angle detection device formed in such a way is installed in an automobile by connecting control means 8 to an electronic circuit (not shown) of a vehicle via a connector, a lead (not shown), and the like and inserting the shaft of the steering into engagement portions 1B of rotation body 1.
With the above configuration, when a steering wheel is rotated, rotation body 1 locked onto the steering shaft is rotated, first detection body 2 is rotated in conjunction with the rotation body 1, and then second detection body 3 is rotated in conjunction with first detection body 2. Thereby, magnets 4A, 5A respectively installed in the centers of first detection body 2 and second detection body 3 are also rotated, and magnetism detection elements 4B, 5B detect changing magnetic forces of magnets 4A, 5A as detection signals. First detection body 2 and second detection body 3 have the difference number of gear teeth and different rotation speed from each other. Thus, data waveforms of magnetism detection elements 4B and 5B become the detection signals in which a cycle is different and a phase is shifted.
Based on the two different detection signals from first detection body 2 and second detection body 3 and the numbers of gear teeth, control means 8 performs predetermined calculation so as to detect a rotation angle of rotation body 1, that is, of the steering wheel. The detected rotation angle is outputted to the electronic circuit of the automobile and various controls of the vehicle are performed.
It should be noted that for example, Unexamined Japanese Patent Publication No. 2009-236515 is known as the related art of the invention of the present application.